Rainbow Electronics W90N745CDG - Manual (Page 99)

W90N745CD/W90N745CDG
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EMC Descriptors
A link-list data structure named as descriptor is used to keep the control, status and data
information of each frame. Through the descriptor, CPU and EMC exchange the information for frame
reception and transmission.
Two different descriptors are defined in W90N745. One named as Rx descriptor for frame
reception and the other names as Tx descriptor for frame transmission. Each Rx descriptor consists of
four words. There is much information kept in the descriptors and details are described as below.
6.5.1.1. Rx Buffer Descriptor
3
1 3
0 2
9 1
6 1
5
0
O Rx Status Receive Byte Count
Receive Buffer Starting Address BO
Reserved
Next Rx Descriptor Starting Address
Rx Descriptor Word 0
31 30 29 28 27 26 25 24
Owner Reserved
23 22 21 20 19 18 17 16
Reserved RP ALIE RXGD PTLE Reserved CRCE RXINTR
15 14 13 12 11 10 9 8
RBC
7 6 5 4 3 2 1 0
RBC
Owner [31:30]: Ownership
The ownership field defines which one, the CPU or EMC, is the owner of each Rx descriptor. Only the
owner has right to modify the Rx descriptor and the others can read the Rx descriptor only.
00: The owner is CPU
01: Undefined
10: The owner is EMC
11: Undefined
If the O=2’b10 indicates the EMC RxDMA is the owner of Rx descriptor and the Rx descriptor is
available for frame reception. After the frame reception completed, if the frame needed NAT
translation, EMC RxDMA modify ownership field to 2’b11. Otherwise, the ownership field will be
modified to 2’b00.